I remember the Mutator....at the time I thought it was expensive but I never did hear it, Im sure it was worth it. Good for ambient, why not. Its a big unit, how much rack space do you have?

I used to have the waldorf D pole filter plugin that worked well for me....waldorf have recently released the 2 pole, actually this maybe a re release, I think there was a hardware version sometime back, anyway its seems versatile and has a small footprint @ 200 euros.